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Topic Review (Newest First)

12-29-2012 01:21 PM

MARTINSR

And the point is alignment can be very complex so it is best to not try to redesign, go with the standard and you are going to be good.

Brian

12-29-2012 01:16 PM

timothale

racing suspension

When Bruce Cambern, retired Head of Ford SVO, set the Track Record on the Road Race Course at MIS all 4 wheels on his 427 Cobra were pointing different directions. Each wheel set for optimum geometry where it need to be for various part of the track where that wheel had the most effect , comprimised to not reduce the total lap time. He used different settings for the various tracks he raced. This Discussion all started when were were giving advice on how to best build a straight axle street car.

12-29-2012 01:06 PM

MARTINSR

Quote:

Originally Posted by techron

Now for race cars or circle track cars, Once again (who cares??) Tires are a consumable, negative camber comes into play (as the car leans into a turn the tread has to stay centered to the pavement) Now anti ackerman comes into play, the outside tire is much more loaded and theoreticaly has much more traction. So why not turn it more?? It works on dirt track cars when the inside tire is off the ground.

Yeah, I have done ZERO roundy round or road racing so I hadn't a clue but that is exactly how I saw it, and it makes perfect sense. I am glad it was brought up because I learned something, very interesting. You betcha some study is important. When I first started doing alignments, it was after years of autobody and paint repair. I was not good at those geometry and arithmetic issues with it, wasn't my kind of thing. I took home an "Autobodynews" from the shop that had a basics of alignment and read that article over and over and over again, it literally took about a week and a half before I "got" it. Included angle, oh my God I just couldn't understand what that was. All I know is that education helped so much with collision repair, that is what we were doing not alignments like a tire shop. We were doing alignments for diagnosis for damage as well as of course proper alignment at the completion of the job. Knowing all that stuff helped so much! I still don't know a whole lot, it's pretty limited to what I just described but damn it helped a lot, so learning even more of course would be even better.

Great Link, actually the best link ever related to this thread. A little book learnin is not a bad thing. My point exactly, this is what I learned in college back in the late 60s, that article almost looks like the text book I had to read when I took a quarter of "steering and suspension". Any car when in a turn rotates around a theoretical center point, the inside tire has to turn at smaller radius than the outside tire so both follow that point.

As you guys know all cars are aligned with a slight toe in when going straight ahead (1/16-1/8 or whatever) any toe out will make the car wander. When I used to do alignments I would always make sure all the steering linkage was tight/correct or refuse to do it. I would also in the first step make sure the steering box was exactly centered (there is a high spot on the gears when the box is centered with increasing clearance as you go to right or left lock).

Ackerman changes that slight toe in to toe out and the toe out increases as the turn radius decreases. I went so far as after an alignment I would slide under under the alignment rack with the tires straight ahead and push the front of the tires out to simulate tire drag on the road te see if there was any change from the slight toe in specs to toe out (any of you guys ever do that??? I think not, it was my own developed process) I would compensate, very rarely and never much to keep toe in within spec to insure a straight tracking car and a happy customer.

Now we are talking older cars here, SLCA cars (short long control arms) not strut rod cars like now.

Racing be damned, the car companies were looking at tire life in production cars(front tire life)
Who any mom or pop would buy a Ford/chev/chry car that wore out the front tires in 4000 miles over and over???

Thus ackerman, the SLCA, Camber would change as the car moved up and down but the tires would not scrub, they would just rotate around the center lines of the upper and lower ball joints, just like the KPA on solid axel cars.

Now for race cars or circle track cars, Once again (who cares??) Tires are a consumable, negative camber comes into play (as the car leans into a turn the tread has to stay centered to the pavement) Now anti ackerman comes into play, the outside tire is much more loaded and theoreticaly has much more traction. So why not turn it more?? It works on dirt track cars when the inside tire is off the ground.

So why not, because I build small block aluminum headed C2 vettes with big block sway bars, they all handle like race karts

12-28-2012 10:39 AM

MARTINSR

Quote:

Originally Posted by OneMoreTime

Well some guys are satisfied with Rustoleum and others want a good paint job..Same with handling..Some guys are happy to keep it between the lines on the way to the rod run and others want to get the car to be the best it can be..Your choice..

Sam

Yep, you are right on the money. And not only what a some guys want, but some cars, they are all different, as long as the builder understands and it meets his expectations. Where a guy may build a knock out show car, the next one may be rough as hell being the expectations are different. It doesn't mean he can't build the super nice car, he did before, but on this particular car his expectations have changed.

Brian

12-28-2012 10:17 AM

OneMoreTime

Well some guys are satisfied with Rustoleum and others want a good paint job..Same with handling..Some guys are happy to keep it between the lines on the way to the rod run and others want to get the car to be the best it can be..Your choice..

Sam

12-28-2012 09:55 AM

MARTINSR

Sam, we aren't talking about "at the track", we are talking super basics on the road. "At the track", holy cow you are talking some serious complexity when it comes to alignment and chassis design. I know NOTHING about the subject and when I start reading something like that link I posted ackermann use in racing I am blown away like I am trying to read another language. But with some study I would get it.

With what we are talking about, it hasn't a thing to do with at the track.

Brian

12-28-2012 09:37 AM

OneMoreTime

Moderators Note: When I see you guys at the track and running up front then I will be more likely believe you when it comes to chassis setup. For the guys interested we adjust everything on a chassis in search of that optimal setup that uses the tire to full advantage. Nuff said!!

Sam

12-28-2012 08:19 AM

timothale

suspension design

An old friend of mine, Bruce Cambern, Retired head of Ford SVO, Still races his Cobra, Won the Optima in 2009 , 3 firsts and a second, they told him he couldn't bring it back. He has redesigned and built new suspensions a couple times, and It gets complicated but his designs work. basic geometry vs the forces loaded on parts.

12-27-2012 05:46 PM

2old2fast

Good Lord Randy, I thought I was antagonistic !! Just because something "works" doesn't make it right . On a liteweight vehicle w /small front tires , you may not be able to discern any bad handling characteristics , however that still doesn't make the design "right". Quit battling windmills !!! SHEESH

dave

12-27-2012 03:32 PM

MARTINSR

What am I getting at Randy, why don't you tell me?

Brian

12-27-2012 03:31 PM

NEW INTERIORS

Quote:

Originally Posted by MARTINSR

Yeah, that's my intention is to fool people. How about the other people who have posted here supporting correct akermann, are they "fooling" people too? Honestly Randy, you need to take an inward look buddy.

Brian

You do know what I'm getting at..
And it isn't about this thread.. You can try turning it around all you want..

12-27-2012 03:31 PM

MARTINSR

Wow, this gets so friggin deep it isn't funny, it's over my head. Randy, a little reading is always good. You posted that quote saying how some race cars use a opposite ackermann, with a little reading it gets explained (?) sort of that is because it is a VERY complicated subject. Damn interesting though.

Costin &Phipps, "Racing & Sports Car Chassis Design", 1961. For performance and racing cars, they recommended a small amount of anti-Ackerman, and did not discuss any circumstance where Ackerman might be used. "Owing to weight transfer, the outside wheel always runs at a higher loading than the inside wheel, and therefore higher slip angles, which necessitate greater lock".

Carroll Smith, "Tune to Win", 1978. Referring to anti-Ackerman, he writes it "cannot be right". He suggested that racing car steering angles are generally too small for Ackerman to build, and that in the mid corner, the inside tyre is not sufficiently loaded for it to have much affect anyway (meaning for Ackerman effect - in general consideration of inside tyre grip is a major focus for set up). For corner entry he prefered to use small amount of static toe out and/or, interestingly, small amount of bumpsteer toe out in bump. Because of the difficulty of predicting dynamic ride height side to side, it may be preferable to run the static toe out required with zero bump steer. Those teams with wheel position sensors and data logging could tell for sure. "Engineer in Your Pocket", 1998. No mention of Ackerman. This is significant. Twenty years after "Tune to Win" Carroll Smith must have considered Ackerman adjustment still only a small part of set up.

Don Alexander, "Performance Handling", 1991. He writes that anti-Ackerman was used in earlier years. But that by the 90's, "Ackerman steering has returned, often exceeding 100 percent geometry", eg for vehicles with high aero down force. However, he has got his explanation of the slip angle effect the wrong way round, and does not expand further. Finally, he says Ackerman is a design element, not a tuning tool the racer will use.

Paul Valkenburg, "Race Car Engineering & Mechanics", 1992. Taking into account the slip angles, "at first glance it might seem" ..."Ackerman steering may be a disadvantage. On the other hand, scientifically obtained tyre data tends to indicate that the lighter the tyre load, the higher the the slip angle required for peak cornering power. This would indicate that Ackerman is in fact usefull in racing cars. " ........."although there probably isn't enough steering motion to have a significant effect. Only your skid pad or test track will tell for sure."

Allan Staniforth, "Competition Car Suspension", 1999. Writing about inside tyre grip he says "My own view, not applying to Ackerman alone, is that any single thing that helps the contact patch do a better job and enjoy a happier existence has to be worth any trouble to achieve." He does not say when, or under what conditions, he would use Ackerman. Later he did an article in one of the technical mags (or was it Simon McBeath?) where he got very keen on Ackerman, and did some testing on a hill climb car. Unfortunately, I can't find the magazine.

Eric Zapletal, "Race Car Engineering" magazine, August 2001. This is part 3 of a series on "Ackerman Explained". He offers a number of "kinematic steer angle curves", representing steering systems with a lot of Ackerman, for various slip angles. At the end of the article he does give some further clues as to how Ackermen may be used. He points out how the car will turn by braking one side of the vehicle - tanks, bulldozers and other "skid-steer"' vehicles are an examples where it is the only steering mechanism. He points out that modern Vehicle Stability Systems (VCS) use the ABS braking system to brake an individual wheel to counter the yaw motion of the vehicle and control oversteer and understeer. "One of the easiest ways to take advantage of this yawing power (in racing cars) is to use dynamic-toe changes. Dynamic toe out of the front wheels generates just the right sort of differential- longitudinal forces that help yaw the vehicle into the corner." I think he is saying if the inside front tyre drag is a bit more than the outside, this will help turn the car into the corner.

Brian.. You have a lot of people fooled here.. But YOU know I can see right through you..

Yeah, that's my intention is to fool people. How about the other people who have posted here supporting correct akermann, are they "fooling" people too? Honestly Randy, you need to take an inward look buddy.

Brian

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